draft-ietf-sieve-mime-loop-02.txt   draft-ietf-sieve-mime-loop-03.txt 
Internet Engineering Task Force T. Hansen Internet Engineering Task Force T. Hansen
Internet-Draft AT&T Laboratories Internet-Draft AT&T Laboratories
Intended status: Standards Track C. Daboo Intended status: Standards Track C. Daboo
Expires: September 19, 2007 Apple Computer Expires: January 9, 2008 Apple Computer
March 18, 2007 July 8, 2007
SIEVE Email Filtering: MIME part Tests, Iteration, Replacement and Sieve Email Filtering: MIME part Tests, Iteration, Extraction,
Enclosure Replacement and Enclosure
draft-ietf-sieve-mime-loop-02.txt draft-ietf-sieve-mime-loop-03
Status of this Memo Status of this Memo
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applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on September 19, 2007. This Internet-Draft will expire on January 9, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The SIEVE email filtering language has no way to examine individual The Sieve email filtering language has no way to examine individual
MIME parts or any way to manipulate those individual parts. However, MIME parts or any way to manipulate those individual parts. However,
being able to filter based on MIME content is important. This being able to filter based on MIME content is important. This
document defines extensions for these needs. document defines extensions for these needs.
Note Note
This document is being discussed on the MTA-FILTERS mailing list, This document is being discussed on the MTA-FILTERS mailing list,
ietf-mta-filters@imc.org. ietf-mta-filters@imc.org.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Sieve Loops . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Changes to Sieve tests . . . . . . . . . . . . . . . . . . . . 4
4.1. Test "header" . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Test "address" . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Test "exists" . . . . . . . . . . . . . . . . . . . . . . 7
5. Action Replace . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Action Enclose . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Action extract_text . . . . . . . . . . . . . . . . . . . . . 9
8. Sieve Capability Strings . . . . . . . . . . . . . . . . . . . 9
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 10
9.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
11. Security Considerations . . . . . . . . . . . . . . . . . . . 12
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
13. Change History (to be removed prior to publication as an
RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. draft-ietf-sieve-mime-02 . . . . . . . . . . . . . . . . . 14
13.2. draft-ietf-sieve-mime-01 . . . . . . . . . . . . . . . . . 14
13.3. draft-ietf-sieve-mime-00 . . . . . . . . . . . . . . . . . 14
13.4. draft-hansen-sieve-loop-01 . . . . . . . . . . . . . . . . 14
13.5. draft-hansen-sieve-loop-02 . . . . . . . . . . . . . . . . 14
13.6. draft-hansen-sieve-loop-03 . . . . . . . . . . . . . . . . 15
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
14.1. Normative References . . . . . . . . . . . . . . . . . . . 15
14.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
1. Introduction 1. Introduction
SIEVE scripts are used to make decisions about the disposition of an Sieve scripts are used to make decisions about the disposition of an
email message. The base SIEVE specification, email message. The base Sieve specification,
[I-D.ietf-sieve-3028bis], defines operators for looking at the [I-D.ietf-sieve-3028bis], defines operators for looking at the
message headers, such as addresses and the subject. Other extensions message headers, such as addresses and the subject. Other extensions
provide access to the body of the message ([I-D.ietf-sieve-body]), or provide access to the body of the message ([I-D.ietf-sieve-body]), or
allow you to manipulate the header of the message allow you to manipulate the header of the message
([I-D.ietf-sieve-editheader]). But none of these extensions take ([I-D.ietf-sieve-editheader]). But none of these extensions take
into account that MIME messages ([RFC2045]) are often complex into account that MIME messages ([RFC2045]) are often complex
objects, consisting of many parts and sub-parts. This extension objects, consisting of many parts and sub-parts. This extension
defines mechanisms for performing tests on MIME body parts, looping defines mechanisms for performing tests on MIME body parts, looping
through the MIME body parts, changing the contents of a MIME body through the MIME body parts, extracting information from a MIME body
part, and enclosing the message with a wrapper. part, changing the contents of a MIME body part, and enclosing the
entire message with a wrapper.
2. Conventions Used in This Document 2. Conventions Used in This Document
Conventions for notations are as in [I-D.ietf-sieve-3028bis] section Conventions for notations are as in [I-D.ietf-sieve-3028bis] section
1.1. 1.1.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. SIEVE Loops 3. Sieve Loops
The base SIEVE language has no looping mechanism. Given that The base Sieve language has no looping mechanism. Given that
messages may contain multiple parts, in order to support filters that messages may contain multiple parts, in order to support filters that
apply to any and all parts, we introduce a new control command: apply to any and all parts, we introduce a new control command:
"for_every_part", which is an iterator that walks though every MIME "for_every_part", which is an iterator that walks though every MIME
part of a message, including nested parts, and applies the commands part of a message, including nested parts, and applies the commands
in the specified block to each of them. The iterator will start with in the specified block to each of them. The iterator will start with
the first MIME part (as its current context) and will execute a the first MIME part (as its current context) and will execute a
command block (SIEVE commands enclosed by { ...}). Upon completion command block (Sieve commands enclosed by { ...}). Upon completion
of this command block, the iterator advances to the next MIME part of this command block, the iterator advances to the next MIME part
(as its current context) and executes the same command block again. (as its current context) and executes the same command block again.
The iterator can be terminated prematurely by a new SIEVE command, The iterator can be terminated prematurely by a new Sieve command,
"break". "break".
Usage: for_every_part block Usage: for_every_part block
Usage: break; Usage: break;
"for_every_part" commands can be nested inside other "for_every_part" "for_every_part" commands can be nested inside other "for_every_part"
commands. When this occurs, the nested "for_every_part" iterates commands. When this occurs, the nested "for_every_part" iterates
over the MIME parts contained within the MIME part current being over the MIME parts contained within the MIME part current being
targeted by the nearest enclosing "for_every_part" command. If that targeted by the nearest enclosing "for_every_part" command. If that
MIME part is a terminal MIME part (i.e. does not contain other MIME MIME part is a terminal MIME part (i.e. does not contain other MIME
parts) then the nested "for_every_loop" is simply ignored. parts) then the nested "for_every_loop" is simply ignored.
SIEVE implementations MAY limit the number of nested loops that occur Sieve implementations MAY limit the number of nested loops that occur
within one another, however they MUST support at least one nested within one another, however they MUST support at least one nested
loop inside another loop. loop inside another loop.
4. Changes to SIEVE tests 4. Changes to Sieve tests
This specification extends the base SIEVE "header", "address" and This specification extends the base Sieve "header", "address" and
"exists" tests to support targeting those tests at a specific MIME "exists" tests to support targeting those tests at a specific MIME
part or at all MIME parts in the enclosing scope. part or at all MIME parts in the enclosing scope.
4.1. Test "header" 4.1. Test "header"
The "header" test is extended with the addition of a new ":mime" The "header" test is extended with the addition of a new ":mime"
tagged argument, which takes a number of other arguments. tagged argument, which takes a number of other arguments.
Usage: header [:mime] [:anychild] [MIMEOPTS] Usage: header [:mime] [:anychild] [MIMEOPTS]
[COMPARATOR] [MATCH-TYPE] [COMPARATOR] [MATCH-TYPE]
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Implementations MAY also impose restrictions on what addresses can be Implementations MAY also impose restrictions on what addresses can be
specified in a ":from" parameter; it is suggested that values that specified in a ":from" parameter; it is suggested that values that
fail such a validity check simply be ignored rather than causing the fail such a validity check simply be ignored rather than causing the
replace action to fail. Implementations MUST preserve the previous replace action to fail. Implementations MUST preserve the previous
From header as an Original-From header. From header as an Original-From header.
6. Action Enclose 6. Action Enclose
Usage: enclose <:subject string> <:headers string-list> string Usage: enclose <:subject string> <:headers string-list> string
A new SIEVE action command is defined to allow an entire message to A new Sieve action command is defined to allow an entire message to
be enclosed as an attachment to a new message. NB: The following be enclosed as an attachment to a new message. After enclosure,
statement may be controversial: This enclose action takes precedence subsequent actions affecting the message header or content use the
over all other message modifications, such as "replace". If multiple newly create message instead of the original message; this means that
"enclose" actions are executed by a script, only the text specified any use of a "replace" action or other similar actions should be
on the last one is used when creating the enclosed message. This executed before the "enclose" action.
action does not affect messages that are forwarded via a "redirect"
action. If multiple "enclose" actions are executed by a script, only the text
specified on the last one is used when creating the enclosed message.
This action does not affect messages that are forwarded via a
"redirect" action.
Specifically, the original message becomes a multipart/mixed message Specifically, the original message becomes a multipart/mixed message
with two parts: a text/plain portion with the string argument as its with two parts: a text/plain portion with the string argument as its
body, and a message/rfc822 portion with the original message body, and a message/rfc822 portion with the original message
enclosed. The Content-Type: header field becomes multipart/mixed. enclosed. The Content-Type: header field becomes multipart/mixed.
The Subject: header is specified by the :subject argument. Any The Subject: header is specified by the :subject argument. Any
headers specified by :headers are copied from the old message into headers specified by :headers are copied from the old message into
the new message. NB: The following statement may be controversial: the new message. If not specified by :headers, Date: and From:
If not specified by :headers, Date: and From: headers should be headers should be synthesized to reflect the current date and the
synthesized to reflect the current date and the user running the user running the Sieve action.
SIEVE action.
7. SIEVE Capability Strings 7. Action extract_text
A SIEVE implementation that defines the "for_every_part" and "break" Usage: extract_text [MODIFIER] [":first" number] <varname: string>
The extract_text action may be used within the context of a
"for_every_part" loop. It stores at most :first bytes of the current
MIME body part in the variable identified by varname. If the :first
parameter is not present, the whole content of the current MIME body
part is stored. In either case the actually stored data MAY be
truncated to conform to implementation specific limit on variable
length and/or on MIME body part length. QUESTION: What do we do if
the Content-Transfer-Encoding is anything other than 7bit?
If extract_text is used outside the context of a "for_every_part"
loop, the action will set the variable identified by varname to the
empty string.
Modifiers are applied on the extracted text before it is stored in
the variable. See [I-D.ietf-sieve-variables] for details.
8. Sieve Capability Strings
A Sieve implementation that defines the "for_every_part" and "break"
actions will advertise the capability string "for_every_part". actions will advertise the capability string "for_every_part".
A SIEVE implementation that defines the ":mime" tagged arguments to A Sieve implementation that defines the ":mime" tagged arguments to
the "header", "address" and "exists" commands will advertise the the "header", "address" and "exists" commands will advertise the
capability string "mime". capability string "mime".
A SIEVE implementation that defines the "replace" action will A Sieve implementation that defines the "replace" action will
advertise the capability string "replace". advertise the capability string "replace".
A SIEVE implementation that defines the "enclose" action will A Sieve implementation that defines the "enclose" action will
advertise the capability string "enclose". advertise the capability string "enclose".
8. Examples A Sieve implementation that defines the "extract_text" action will
advertise the capability string "extract_text". Note that to be
useful, the "extract_text" action also requires the "variables"
[I-D.ietf-sieve-variables] and "mime" capabilities.
8.1. Example 1 9. Examples
A SIEVE script to replace all the Windows executable attachments in a 9.1. Example 1
A Sieve script to replace all the Windows executable attachments in a
message would be: message would be:
require [ "for_every_part", "mime", "replace" ]; require [ "for_every_part", "mime", "replace" ];
for_every_part for_every_part
{ {
if ( anyof ( if ( anyof (
header :mime :contenttype :is "Content-Type" "application/exe", header :mime :contenttype :is "Content-Type" "application/exe",
header :mime :param "filename" header :mime :param "filename"
["Content-Type", "Content-Disposition"] :matches "*.com" ) ["Content-Type", "Content-Disposition"] :matches "*.com" )
{ {
replace "Executable attachment removed by user filter"; replace "Executable attachment removed by user filter";
} }
} }
8.2. Example 2 9.2. Example 2
A SIEVE script to warn the user about executable attachment types A Sieve script to warn the user about executable attachment types
would be: would be:
require [ "for_every_part", "mime", "enclose" ]; require [ "for_every_part", "mime", "enclose" ];
for_every_part for_every_part
{ {
if header :mime :param "filename" if header :mime :param "filename"
["Content-Type", "Content-Disposition"] :matches ["Content-Type", "Content-Disposition"] :matches
["*.com", "*.exe", "*.vbs", "*.scr", ["*.com", "*.exe", "*.vbs", "*.scr",
"*.pif", "*.hta", "*.bat", "*.zip" ] "*.pif", "*.hta", "*.bat", "*.zip" ]
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that can infect your computer and potentently damage your data that can infect your computer and potentently damage your data
Before clicking on these message attachments, you should verify Before clicking on these message attachments, you should verify
with the sender that this message was sent by them and not a with the sender that this message was sent by them and not a
computer virus. computer virus.
"; ";
break; break;
} }
} }
9. Acknowledgements 9.3. Example 3
A Sieve script to extract subject and text out of messages from the
boss
require ["mime", "variables", "extract_text"];
if header :contains "from" "boss@example.org"
{
# :matches is used to get the value of the Subject header
if header :matches "Subject" "*"
{
set "subject" "${1}";
}
# extract the first 100 bytes of the first text/* part
for_every_part
{
if header :mime :type :is "Content-Type" "text"
{
extract_text :first 100 "msgcontent";
break;
}
}
# if it's not a 'for your information' message
if not header :contains "subject" "FYI:"
{
# do something using ${subject} and ${msgcontent}
# such as sending a notification using a notification extion
}
}
10. Acknowledgements
Comments from members of the MTA Filters Working Group, in particular Comments from members of the MTA Filters Working Group, in particular
Ned Freed, Nigel Swinson and Mark Mallett, are gratefully Ned Freed, Nigel Swinson, Mark Mallett and Alexey Melnikov, are
acknowledged. gratefully acknowledged.
10. Security Considerations 11. Security Considerations
To be provided The "enclose" action creates an entirely new message, as compared to
just redirecting or forwarding the existing message. Therefore, any
site policies applicable to message submission should be enforced
here.
11. IANA Considerations The looping specification specified here provides easier access to
information about the message contents, which may also be achieved
through other sieve tests. This is not believed to raise any
additional security issues beyond those for the Sieve "envelope" and
"body" tests.
The system MUST be sized and restricted in such a manner that even
malicious use of mime part matching does not deny service to other
users of the host system.
Any change in a message content may interfere with digital signature
mechanisms that include the body in the signed material.
All of the security considerations given in the base Sieve
specification also apply to these extensions.
12. IANA Considerations
The Original-Subject: and Original-From: headers are to be registered The Original-Subject: and Original-From: headers are to be registered
in the Permanent Message Header Fields table. in the Permanent Message Header Fields table.
12. Change History (to be removed prior to publication as an RFC) The following template specifies the IANA registration of the Sieve
extensions specified in this document:
12.1. draft-ietf-sieve-mime-02 To: iana@iana.org Subject: Registration of new Sieve extensions
Capability name: for_every_part
Description: adds the "for_every_part" and "break" actions for
iterating through MIME parts of a message.
Capability name: mime
Description: adds ":mime" tagged arguments to the "header", "address"
and "exists" commands.
Capability name: replace
Description: adds the "replace" action for replacing a MIME body part
of a message.
Capability name: enclose
Description: adds the "enclose" action for enclosing a message with a
wrapper.
Capability name: extract_text
Description: adds the "extract_text" action for extracting text from
a MIME body part.
RFC number: RFC XXXX
Contact address: The Sieve discussion list
<ietf-mta-filters@imc.org>.
This information should be added to the list of sieve extensions
given on http://www.iana.org/assignments/sieve-extensions.
13. Change History (to be removed prior to publication as an RFC)
13.1. draft-ietf-sieve-mime-02
minor syntax glitches in examples minor syntax glitches in examples
Add clarification on "replace" affecting subsequent for_every_part Add clarification on "replace" affecting subsequent for_every_part
loops? loops?
Add IANA considerations for Original-Subject: and Original-From:. Add IANA considerations for Original-Subject: and Original-From:.
Add note on "enclose" creating From: and Date: headers. Add note on "enclose" creating From: and Date: headers.
12.2. draft-ietf-sieve-mime-01 13.2. draft-ietf-sieve-mime-01
what happens when nested for_every_loop's what happens when nested for_every_loop's
a "mime" shorthand for testing the type/subtype, without requiring a "mime" shorthand for testing the type/subtype, without requiring
interactions with variables interactions with variables
notifications notifications
notifications to calendar service notifications to calendar service
address tests, exists tests address tests, exists tests
mimeheader, mimeparameter tests mimeheader, mimeparameter tests
12.3. draft-ietf-sieve-mime-00 13.3. draft-ietf-sieve-mime-00
Changed title and text to emphasize MIME Tests. Changed title and text to emphasize MIME Tests.
Changed for.every.part to for_every_part. Changed for.every.part to for_every_part.
Added :anychild to mime test. Default is to use the current context Added :anychild to mime test. Default is to use the current context
or outer envelope; specifying :anychild will look at all children. or outer envelope; specifying :anychild will look at all children.
Added clarifications to replacing parts affecting the structure. Added clarifications to replacing parts affecting the structure.
Added :mime option to replace, ala draft-ietf-sieve-vacation-06. Added :mime option to replace, ala draft-ietf-sieve-vacation-06.
Various other minor nit fixes. Various other minor nit fixes.
12.4. draft-hansen-sieve-loop-01 13.4. draft-hansen-sieve-loop-01
Merged with draft-daboo-sieve-mime-00.txt. Merged with draft-daboo-sieve-mime-00.txt.
12.5. draft-hansen-sieve-loop-02 13.5. draft-hansen-sieve-loop-02
Update to 3028bis reference. Update to 3028bis reference.
Added 2119 conventions section. Added 2119 conventions section.
Terminology/title tweaks. Terminology/title tweaks.
Added informative references to body and editheader extensions. Added informative references to body and editheader extensions.
Added description of nested loops. Added description of nested loops.
Replaced mime test by extensions to header, address and exists Replaced mime test by extensions to header, address and exists
tests. tests.
13. References 13.6. draft-hansen-sieve-loop-03
13.1. Normative References after enclosure, subsequent actions affect newly created message
synthesis of Date/From headers by the enclose action is no longer
controversial
Filled in Security Considerations
Picked up extract_text action from draft-ietf-sieve-notify
Expanded the IANA considerations section
14. References
14.1. Normative References
[I-D.ietf-sieve-3028bis] [I-D.ietf-sieve-3028bis]
Showalter, T. and P. Guenther, "Sieve: An Email Filtering Showalter, T. and P. Guenther, "Sieve: An Email Filtering
Language", draft-ietf-sieve-3028bis-12 (work in progress), Language", draft-ietf-sieve-3028bis-12 (work in progress),
February 2007. February 2007.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text", Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996. RFC 2047, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, [RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001. April 2001.
13.2. Informative References 14.2. Informative References
[I-D.ietf-sieve-body] [I-D.ietf-sieve-body]
Guenther, P. and J. Degener, "Sieve Email Filtering: Body Guenther, P. and J. Degener, "Sieve Email Filtering: Body
Extension", draft-ietf-sieve-body-06 (work in progress), Extension", draft-ietf-sieve-body-06 (work in progress),
February 2007. February 2007.
[I-D.ietf-sieve-editheader] [I-D.ietf-sieve-editheader]
Guenther, P. and J. Degener, "Sieve Email Filtering: Guenther, P. and J. Degener, "Sieve Email Filtering:
Editheader Extension", draft-ietf-sieve-editheader-08 Editheader Extension", draft-ietf-sieve-editheader-08
(work in progress), March 2007. (work in progress), March 2007.
[I-D.ietf-sieve-variables]
Homme, K., "Sieve Extension: Variables",
draft-ietf-sieve-variables-08 (work in progress),
December 2005.
Authors' Addresses Authors' Addresses
Tony Hansen Tony Hansen
AT&T Laboratories AT&T Laboratories
200 Laurel Ave. 200 Laurel Ave.
Middletown, NJ 07748 Middletown, NJ 07748
USA USA
Email: tony+sieveloop@maillennium.att.com Email: tony+sieveloop@maillennium.att.com
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